The present invention relates to drawbars for agricultural tractors.
Farm tractors are being used more frequently for transporting large bulk carriers. Newer tractors have top speeds of from 80 to 100 kph making their use for transportation quite practical. It is therefore often found more cost effective to use a tractor to transport grain, fertilizer, liquid manure, feed etc. rather than purchasing a truck. In some parts of the world this is now a common practice. In North America it is becoming more so.
A tractor generally has a single drawbar that is designed to pull agricultural implements. These implements generally do not exert large vertical loads on the drawbar. When used for towing bulk carriers, however the usual tractor drawbar may be vertically overloaded and may fail. In addition, loose drawbar couplings in such environments are hard on the hitch parts and result in rapid wear.
One attempt to resolve this problem added a bolt-on reinforcement strap to the drawbar. That was positioned, in use, below the drawbar support plate on which the drawbar rests. This has not proven satisfactory. The bottom reinforcement creates concerns over adequate ground clearance and it does not deal with the high shear stresses where the drawbar is cantilevered off the support plate. In addition, failures commonly occur at those places where angular offsets are formed in the drawbar, usually to provide the requisite spacing from a hammer strap mounted on top of the drawbar.
The present invention proposes a novel drawbar that is intended to address these problems.
According to the present invention there is provided a tractor drawbar comprising
an elongate forward drawbar section of substantially uniform rectangular cross section;
an elongate second drawbar section extending rearwardly from the forward drawbar section, the second drawbar section having substantially the same vertical thickness as the forward drawbar section and a width substantially greater than the width of the forward drawbar section;
an elongate trailing drawbar section extending rearwardly from the forward drawbar section, the second drawbar section having substantially the same vertical thickness as the forward drawbar section and a width substantially the same as the width of the forward drawbar section;
two transition sections between the second drawbar section and the forward and trailing drawbar sections respectively; and
two angular offsets in the second drawbar section such that the trailing drawbar section is parallel to and offset downwardly from the second drawbar section.
This structure can be used as a conventional tractor drawbar for pulling implements in the field. It has however, sufficient strength and stiffness that it can also be used for transporting bulk cargo. The positions of highest stress are all located in the wide second section, so that the additional transport loads can be handled. The drawbar, being one piece, can easily be installed by sliding it into place in the same way as a conventional drawbar.
According to another aspect of the present invention there is provided a method of manufacturing the drawbar, which comprises:
flame cutting a blank for the drawbar;
die forming the angular offsets in the blank;
heat treating the formed blank;
forming pivot pin holes in the forward section of the blank and a draw pin hole in the trailing section.
It has been found that the flame cutting process may cause the properties of the resultant product to be outside of the required specifications. This problem may be resolved by machining the drawbar from bar stock.
Thus, according to a further aspect of the present invention there is provided a method of manufacturing the drawbar, which comprises:
machining a blank for the drawbar;
die forming the angular offsets in the blank;
heat treating the formed blank;
forming pivot pin holes in the forward section of the blank and a draw pin hole in the trailing section.
Preferably, the blank is quenched after die forming.